Schizophrenia susceptibility loci on chromosomes 13q32 and 8p21

Schizophrenia is a common disorder characterized by psychotic symptoms; diagnostic criteria have been established. Family, twin and adoption studies suggest that both genetic and environmental factors influence susceptibility (heritability is approximately 71%; ref. 2), however, little is known about the aetiology of schizophrenia. Clinical and family studies suggest aetiological heterogeneity. Previously, we reported that regions on chromosomes 22, 3 and 8 may be associated with susceptibility to schizophrenia, and collaborations provided some support for regions on chromosomes 8 and 22 (refs 9-13). We present here a genome-wide scan for schizophrenia susceptibility loci (SSL) using 452 microsatellite markers on 54 multiplex pedigrees. Non-parametric linkage (NPL) analysis provided significant evidence for an SSL on chromosome 13q32 (NPL score=4.18; P=0.00002), and suggestive evidence for another SSL on chromosome 8p21-22 (NPL=3.64; P=0.0001). Parametric linkage analysis provided additional support for these SSL. Linkage evidence at chromosome 8 is weaker than that at chromosome 13, so it is more probable that chromosome 8 may be a false positive linkage. Additional putative SSL were noted on chromosomes 14q13 (NPL=2.57; P=0.005), 7q11 (NPL=2.50, P=0.007) and 22q11 (NPL=2.42, P=0.009). Verification of suggestive SSL on chromosomes 13q and 8p was attempted in a follow-up sample of 51 multiplex pedigrees. This analysis confirmed the SSL in 13q14-q33 (NPL=2.36, P=0.007) and supported the SSL in 8p22-p21 (NPL=1.95, P=0.023).

Sequential strategy to identify a susceptibility gene for schizophrenia: report of potential linkage on chromosome 22q12-q13.1: Part 1

To identify genes responsible for the susceptibility for schizophrenia, and to test the hypothesis that schizophrenia is etiologically heterogeneous, we have studied 39 multiplex families from a systematic sample of schizophrenic patients. Using a complex autosomal dominant model, which considers only those with a diagnosis of schizophrenia or schizoaffective disorder as affected, a random search of the genome for detection of linkage was undertaken. Pairwise linkage analyses suggest a potential linkage (LRH = 34.7 or maximum lod score = 1.54) for one region (22q12-q13.1). Reanalyses, varying parameters in the dominant model, maximized the LRH at 660.7 (maximum lod score 2.82). This finding is of sufficient interest to warrant further investigation through collaborative studies.

Schizophrenia: a genome scan targets chromosomes 3p and 8p as potential sites of susceptibility genes

Using a systematically ascertained sample of 57 families, each having 2 or more members with a consensus diagnosis of schizophrenia (DSM-III-R criteria), we have carried out linkage studies of 520 loci, covering approximately 70% of the genome for susceptibility loci for schizophrenia. A two-stage strategy based on lod score thresholds from simulation studies of our sample identified regions for further exploration. In each region, a dense map of highly informative dinucleotide repeat polymorphisms (heterozygosity greater than .70) was analyzed using dominant, recessive, and "affected only" models and nonparametric sib pair identity-by-descent methods. For one region, 8p22-p21, affected sib-pair analyses gave a P value = .0001, corresponding to a lod score approximately equal to 3.00. For 8p22-p21, the maximum two-point lod score occurred using the "affected only" recessive model (ZMAX = 2.35; theta M = theta F); allowing for a constant sex difference in recombination fractions found in reference pedigrees, ZMAX = 2.78 (theta M/theta F = 3). For a second region, 3p26-p24, the maximum two-point lod score was 2.34 ("affected only" dominant model), and the affected sib-pair P value was .01. These two regions are worthy of further exploration as potential sites of susceptibility genes for schizophrenia.

Meta-analysis of 32 genome-wide linkage studies of schizophrenia

A genome scan meta-analysis (GSMA) was carried out on 32 independent genome-wide linkage scan analyses that included 3255 pedigrees with 7413 genotyped cases affected with schizophrenia (SCZ) or related disorders. The primary GSMA divided the autosomes into 120 bins, rank-ordered the bins within each study according to the most positive linkage result in each bin, summed these ranks (weighted for study size) for each bin across studies and determined the empirical probability of a given summed rank (P(SR)) by simulation. Suggestive evidence for linkage was observed in two single bins, on chromosomes 5q (142-168 Mb) and 2q (103-134 Mb). Genome-wide evidence for linkage was detected on chromosome 2q (119-152 Mb) when bin boundaries were shifted to the middle of the previous bins. The primary analysis met empirical criteria for 'aggregate' genome-wide significance, indicating that some or all of 10 bins are likely to contain loci linked to SCZ, including regions of chromosomes 1, 2q, 3q, 4q, 5q, 8p and 10q. In a secondary analysis of 22 studies of European-ancestry samples, suggestive evidence for linkage was observed on chromosome 8p (16-33 Mb). Although the newer genome-wide association methodology has greater power to detect weak associations to single common DNA sequence variants, linkage analysis can detect diverse genetic effects that segregate in families, including multiple rare variants within one locus or several weakly associated loci in the same region. Therefore, the regions supported by this meta-analysis deserve close attention in future studies.

A combined analysis of D22S278 marker alleles in affected sib-pairs: support for a susceptibility locus for schizophrenia at chromosome 22q12. Schizophrenia Collaborative Linkage Group (Chromosome 22)

Several groups have reported weak evidence for linkage between schizophrenia and genetic markers located on chromosome 22q using the lod score method of analysis. However these findings involved different genetic markers and methods of analysis, and so were not directly comparable. To resolve this issue we have performed a combined analysis of genotypic data from the marker D22S278 in multiply affected schizophrenic families derived from 11 independent research groups worldwide. This marker was chosen because it showed maximum evidence for linkage in three independent datasets (Vallada et al., Am J Med Genet 60:139-146, 1995; Polymeropoulos et al., Neuropsychiatr Genet 54:93-99, 1994; Lasseter et al., Am J Med Genet, 60:172-173, 1995. Using the affected sib-pair method as implemented by the program ESPA, the combined dataset showed 252 alleles shared compared with 188 alleles not share (chi-square 9.31, 1df, P = 0.001) where parental genotype data was completely known. When sib-pairs for whom parental data was assigned according to probability were included the number of alleles shared was 514.1 compared with 437.8 not shared (chi-square 6.12, 1df, P = 0.006). Similar results were obtained when a likelihood ratio method for sib-pair analysis was used. These results indicate that may be a susceptibility locus for schizophrenia at 22q12.

Planum temporale asymmetry reversal in schizophrenia: replication and relationship to gray matter abnormalities

OBJECTIVE

The planum temporale, the posterior superior surface of the superior temporal gyrus, is a highly lateralized brain structure involved with language. In schizophrenic patients the authors previously found consistent reversal of the normal left-larger-than-right asymmetry of planum temporale surface area. The original subjects plus new patients and comparison subjects participated in this effort to replicate and extend the prior study.

METHOD

High-resolution magnetic resonance imaging of 28 schizophrenic patients and 32 group-matched normal subjects was performed. The authors measured planum temporale surface area, gray matter volume underlying the planum temporale, and gray matter thickness. Asymmetry indices for areas and volumes were calculated.

RESULTS

Overall gray matter and total brain volume were not significantly smaller in the patients than in the comparison subjects. As previously reported, there was striking reversal of the normal asymmetry for planum temporale surface area in the male and female schizophrenic subjects. Bilaterally, gray matter volume beneath the planum temporale was smaller in the schizophrenic patients, and the gray matter thickness of the right planum temporale was only 50% of the comparison value. Volume of planum temporale gray matter did not show significant asymmetry in either group.

CONCLUSIONS

This study extends the finding of reversed planum temporale surface area asymmetry in schizophrenic patients and clarifies its relationship to underlying gray matter volume. Although right planum temporale surface area is larger than normal in schizophrenia, gray matter volume is less than the comparison value; thus, gray matter thickness is substantially less than normal.

Multicenter linkage study of schizophrenia candidate regions on chromosomes 5q, 6q, 10p, and 13q: schizophrenia linkage collaborative group III

Schizophrenia candidate regions 33-51 cM in length on chromosomes 5q, 6q, 10p, and 13q were investigated for genetic linkage with mapped markers with an average spacing of 5.64 cM. We studied 734 informative multiplex pedigrees (824 independent affected sibling pairs [ASPs], or 1,003 ASPs when all possible pairs are counted), which were collected in eight centers. Cases with diagnoses of schizophrenia or schizoaffective disorder (DSM-IIIR criteria) were considered affected (n=1,937). Data were analyzed with multipoint methods, including nonparametric linkage (NPL), ASP analysis using the possible-triangle method, and logistic-regression analysis of identity-by-descent (IBD) sharing in ASPs with sample as a covariate, in a test for intersample heterogeneity and for linkage with allowance for intersample heterogeneity. The data most supportive for linkage to schizophrenia were from chromosome 6q; logistic-regression analysis of linkage allowing for intersample heterogeneity produced an empirical P value <.0002 with, or P=.0004 without, inclusion of the sample that produced the first positive report in this region; the maximum NPL score in this region was 2.47 (P=.0046), the maximum LOD score (MLS) from ASP analysis was 3.10 (empirical P=.0036), and there was significant evidence for intersample heterogeneity (empirical P=.0038). More-modest support for linkage was observed for chromosome 10p, with logistic-regression analysis of linkage producing an empirical P=. 045 and with significant evidence for intersample heterogeneity (empirical P=.0096).

Season of birth: schizophrenia and bipolar disorder

Studies investigating the association between the risk of schizophrenia and season of birth are reviewed and the association clearly established. This association cannot be explained on the basis of age-incidence or age-prevalence artifacts. Other studies suggest there may be an association between bipolar disorder and season of birth. The leading theory in explaining the season of birth phenomenon is that a seasonal factor (such as viral infection, malnutrition, vitamin deficiency, prenatal or obstetrical complications, or ambient temperature) can damage an infant's brain and thereby predispose the child to later development of psychosis. Evidence suggests that the seasonal effect is associated with a subgroup of schizophrenics who have early onset of psychosis, less genetic loading than other schizophrenics, and better prognosis. Case-control studies are needed comparing winterborn to nonwinter-born schizophrenics.

Reversal of asymmetry of the planum temporale in schizophrenia

OBJECTIVE

The planum temporale is intimately involved in the generation and understanding of language and has been suggested to be a key area affected in schizophrenia. To explore temporal lobe abnormalities in schizophrenia, the authors measured the planum temporale, a normally asymmetric area lying on the superior part of the temporal lobe, in schizophrenic patients.

METHOD

High-resolution magnetic resonance imaging (MRI) scans were obtained for 14 right-handed schizophrenic patients and 14 healthy comparison subjects individually matched for age, sex, handedness, race, and parental socioeconomic status. The surface area of the planum temporale was measured by using MRI reconstruction techniques.

RESULTS

There was striking reversal of the normal asymmetry (left larger than right) in planum temporale surface area in 13 of the schizophrenic patients but in only two of the comparison subjects. However, Heschl's gyrus (primary sensory cortex), which served as an anatomically contiguous nonheteromodal cortical comparison region, showed no difference between the left and right sides in either group. Severity of thought disorder in the patients was related to asymmetry.

CONCLUSIONS

This is a clear demonstration of a reversal of expected symmetry in the brains of right-handed schizophrenic patients, which involves a region of key importance in normal human behavior. The nature of the abnormality strongly suggests that schizophrenia is a neurodevelopmental disorder.

Follow-up of a report of a potential linkage for schizophrenia on chromosome 22q12-q13.1: Part 2

A collaboration involving four groups of investigators (Johns Hopkins University/Massachusetts Institute of Technology; Medical College of Virginia/The Health Research Board, Dublin; Institute of Psychiatry, London/University of Wales, Cardiff; Centre National de la Recherche Scientifique, Paris) was organized to confirm results suggestive of a schizophrenia susceptibility locus on chromosome 22 identified by the JHU/MIT group after a random search of the genome. Diagnostic, laboratory, and analytical reliability exercises were conducted among the groups to ensure uniformity of procedures. Data from genotyping of 3 dinucleotide repeat polymorphisms (at the loci D22S268, IL2RB, D22S307) for a combined replication sample of 256 families, each having 2 or more affected individuals with DNA, were analysed using a complex autosomal dominant model. This study provided no evidence for linkage or heterogeneity for the region 22q12-q13 under this model. We conclude that if this region confers susceptibility to schizophrenia, it must be in only a small proportion of families. Collaborative efforts to obtain large samples must continue to play an important role in the genetic search for clues to complex psychiatric disorders such as schizophrenia.

Search for schizophrenia susceptibility genes

Identification of a gene or genes that contribute to the development of schizophrenia, a complex psychiatric disorder, may be possible through genetic linkage analysis. Although to date no single causative gene has been identified, several chromosomal loci have shown positive linkage results and are under investigation as tentative schizophrenia susceptibility loci. Despite such obstacles as locus heterogeneity among sample populations, epistatic inheritance models, and failure to obtain statistical significance in studies, patterns have emerged that focus research efforts on chromosomes 13, 8, 22, and 6 and 10. Initial heterogeneity analyses suggests that identifiable subgroups of the families may not contribute equally to these linkage findings. Findings on several additional chromosomes await further replication. Future progress in the search for schizophrenia susceptibility genes will require collaboration among researchers from both academia and industry.

Identification of sequence variants and analysis of the role of the catechol-O-methyl-transferase gene in schizophrenia susceptibility

BACKGROUND

Deletions of 1.5-2 MB of chromosome 22q11 have been previously associated with schizophrenia. The deleted region includes proximally the region harboring genes involved in DiGeorge and velocardiofacial syndromes. Distally, it includes the gene for catechol-O-methyl-transferase (COMT), an enzyme that catalyzes the O-methylation of catecholamine neurotransmitters, including dopamine, and which therefore is considered a candidate gene for schizophrenia.

METHODS

We address the issue of a direct involvement of the COMT gene in the development of schizophrenia by employing the first extensive mutational analysis of this gene in a sample of 157 schizophrenia patients and 129 healthy controls, using single-strand conformation polymorphism and chemical cleavage methodologies.

RESULTS

No mutations were found, but several sequence variants were identified, including the genetic polymorphism that underlies the high/low activity of the enzyme (a Val158-->Met change, which results in the creation of an NlaIII restriction site in the low-activity allele). The distribution of the NlaIII genotypes among subsets of schizophrenia patients was analyzed.

CONCLUSIONS

The results presented here argue against a major role of COMT in schizophrenia in general (although a minor effect could not be excluded) and represent a first step toward a more refined delineation of the phenotype/genotype relationship between 22q11 microdeletions and schizophrenia susceptibility.

Genetic heterogeneity in schizophrenia: stratification of genome scan data using co-segregating related phenotypes

Despite considerable effort to identify susceptibility loci for schizophrenia, none have been localized. Multiple genome scans and collaborative efforts have shown evidence for linkage to regions on chromosomes 1q, 5q, 6q, 8p, 13q, 10p and 22q.(1-9) Heterogeneity is likely. We previously mapped schizophrenia susceptibility loci (SSL) to chromosomes 13q32 (P = 0.00002) and 8p21-22 (P= 0.0001) using 54 multiplex pedigrees and suggested linkage heterogeneity. We have now stratified these families based on co-segregating phenotypes in non-schizophrenic first degree relatives (schizophrenia spectrum personality disorders (SSPD); psychotic affective disorders (PAD)). Genome scans were conducted for these phenotypic subgroups of families and broadened affected phenotypes were tested. The SSPD group provided its strongest genome-wide linkage support for the chromosome 8p21 region (D8S1771) using either narrow (non-parametric lod (NPL) P= 0.000002) or broadened phenotypes (NPL P = 0.0000008) and a new region of interest on 1p was identified (P = 0.006). For PAD families, the peak NPL in the genome scan occurred on chromosome 3p26-p24 (P = 0.008). The identification of multiple susceptibility loci for schizophrenia may be enhanced by stratification of families using psychiatric diagnoses of the non-schizophrenic relatives.

Coping strategies, social support, life orientation and health-related quality of life following traumatic brain injury

OBJECTIVE

To study coping strategies, social support and life orientation in patients following moderate and severe traumatic brain injury (TBI) in relation to health-related quality of life.

SUBJECTS

Eighty-five patients with moderate or severe TBI and 68 control persons.

METHODS

Estonian versions of the COPE-D test, the Brief Social Support Questionnaire, the Life Orientation Test and the RAND-36 questionnaire.

RESULTS

Persons with TBI reported using task-oriented and social/emotional support strategies less often and avoidance-oriented strategies more often than control persons (p < 0.05). The social support network, satisfaction with it and optimism as life orientation were lower in the patient group (p < 0.05). Task-oriented coping styles, satisfaction with social support and optimistic life orientation were associated with the majority of the domains of health-related quality of life and resuming work after TBI.

CONCLUSIONS

To achieve effective rehabilitation and to enhance patients' well-being, it is important to improve the quality and amount of social support network, as well as to support patients' adequate coping efforts for promoting an active lifestyle.

Genomewide linkage scan of schizophrenia in a large multicenter pedigree sample using single nucleotide polymorphisms

A genomewide linkage scan was carried out in eight clinical samples of informative schizophrenia families. After all quality control checks, the analysis of 707 European-ancestry families included 1615 affected and 1602 unaffected genotyped individuals, and the analysis of all 807 families included 1900 affected and 1839 unaffected individuals. Multipoint linkage analysis with correction for marker-marker linkage disequilibrium was carried out with 5861 single nucleotide polymorphisms (SNPs; Illumina version 4.0 linkage map). Suggestive evidence for linkage (European families) was observed on chromosomes 8p21, 8q24.1, 9q34 and 12q24.1 in nonparametric and/or parametric analyses. In a logistic regression allele-sharing analysis of linkage allowing for intersite heterogeneity, genomewide significant evidence for linkage was observed on chromosome 10p12. Significant heterogeneity was also observed on chromosome 22q11.1. Evidence for linkage across family sets and analyses was most consistent on chromosome 8p21, with a one-LOD support interval that does not include the candidate gene NRG1, suggesting that one or more other susceptibility loci might exist in the region. In this era of genomewide association and deep resequencing studies, consensus linkage regions deserve continued attention, given that linkage signals can be produced by many types of genomic variation, including any combination of multiple common or rare SNPs or copy number variants in a region.

No evidence for linkage between schizophrenia and markers at chromosome 15q13-14

Freedman et al. [1997: Proc Natl Acad Sci USA 94:587-592] reported linkage in nine multiplex schizophrenia families to markers on chromosome 15, using impaired neuronal inhibition to repeated auditory stimuli (P50), a neurophysiological deficit associated with schizophrenia, as the phenotype. The highest LOD score obtained (5.3 at theta = 0) was for marker D15S1360 mapped to chromosome 15q13-14, less than 120 kb from the alpha7-nicotinic receptor (CHRNA7) gene. The study also reported a small positive LOD score for D15S1360 when examined for linkage to the schizophrenia phenotype. Following these findings, we examined three polymorphic markers (D15S1360, L76630, and ACTC) on chromosome 15q13-14 near the CHRNA7 gene for linkage to schizophrenia, using 54 pedigrees from an independent study. Alleles for these three markers were genotyped and analyzed using parametric and nonparametric methods. No LOD score above 1.00 was obtained for any marker, and affected sib-pair analysis likewise showed no evidence for linkage. We conclude that in our families the region around the CHRNA7 locus does not contain a major locus for susceptibility to schizophrenia.

Schizophrenia: age at onset, gender and familial risk

In a family history study of 366 schizophrenic probands and their 1851 first-degree relatives, we found a relationship between age at onset of psychosis in the male probands and the risk for schizophrenia in their relatives. The relatives of male schizophrenic probands whose onset of psychosis occurred when they were younger than 17 years of age had an increased risk of schizophrenia when compared with the relatives of male probands with an age at onset greater than 17. We did not find an association between age at onset of psychosis in the female probands and familial risk. Cox proportional hazards models permitted us to examine the relationship between age at onset of psychosis in the probands and familial risk while controlling for possible confounding effects.

Current smoking is associated with worse cognitive and adaptive functioning in serious mental illness

OBJECTIVE

Cigarette smoking is highly prevalent among people with bipolar disorder or schizophrenia. Few studies have examined whether smoking history is associated with adaptive functioning among individuals diagnosed with these serious mental illnesses.

METHOD

In a large relatively homogenous cohort of patients with either bipolar disorder (n=363) or schizophrenia (n=400), we investigated the association between cigarette smoking status, intensity, and cumulative exposure and performance on a comprehensive battery of neurocognitive, functional capacity, and informant-rated functional measures. The associations were adjusted for variation in sociodemographic indicators, psychopathologic symptoms, and substance use.

RESULTS

There was an average of 12 pack years of smoking across the sample. People with schizophrenia reported double the rate of current smoking compared to patients with bipolar disorder. Adjusting for demographic covariates, current smokers had worse composite cognitive functioning and poorer functional outcome than past or never smokers. There were no significant differences between never and past smokers, and these effects were evident in both bipolar disorder and schizophrenia.

CONCLUSION

Current smokers with either schizophrenia or bipolar disorder evidence worse cognitive and adaptive functioning functional outcome, even when demographic covariates are considered.

Multicenter linkage study of schizophrenia loci on chromosome 22q

The hypothesis of the existence of one or more schizophrenia susceptibility loci on chromosome 22q is supported by reports of genetic linkage and association, meta-analyses of linkage, and the observation of elevated risk for psychosis in people with velocardiofacial syndrome, caused by 22q11 microdeletions. We tested this hypothesis by evaluating 10 microsatellite markers spanning 22q in a multicenter sample of 779 pedigrees. We also incorporated age at onset and sex into the analysis as covariates. No significant evidence for linkage to schizophrenia or for linkage associated with earlier age at onset, gender, or heterogeneity across sites was observed. We interpret these findings to mean that the population-wide effects of putative 22q schizophrenia susceptibility loci are too weak to detect with linkage analysis even in large samples.

Personality as a predictor of coping efforts in patients with multiple sclerosis

The aim of the study was to explore personality traits as predictors of coping with disease-related distress in patients with multiple sclerosis (MS). All patients with clinically definite MS in a city with a population of approximately 100000 were asked to complete the NEO Personality Inventory and a multidimensional coping inventory (COPE). There was an 83% response rate yielding 49 patients for the study population and 49 controls, matched for age, gender and educational level to the MS-patients, were used as comparison. Only Neuroticism correlated significantly with emotion-focused coping in both groups. Extraversion and Openness to Experience were linked to task-oriented coping strategies in normal controls but not in the MS-group. Agreeableness was associated with avoidance-oriented coping strategies only in the MS-group. Thus, the relation of certain personality characteristics to the choice of strategies for coping with the disease-related distress appear to differ from coping with stressful problems in everyday life. As dispositional characteristics may interfere with adaptive coping responses, analysis of personality traits and coping strategies could contribute while attempting to relieve the consequences of chronic disease on everyday life.

Risk factors in schizophrenia. Season of birth, gender, and familial risk

The risk for schizophrenia among first-degree relatives of schizophrenic probands obtained from an epidemiological sample using family history methods was examined to determine whether month of birth of the proband was associated with familial risk. The results of this study of the first-degree relatives of 106 female schizophrenics and 275 male schizophrenics suggested that the relatives of probands born in the months February to May had the highest risk, although the association between month of birth and familial risk among the male probands was present only for those relatives who had onset of schizophrenia before the age of 30.

Analysis of case-control/family sampling design

A commonly adopted design in genetic epidemiologic studies is the so-called case-control/family sampling design. Here, cases and controls are sampled and response variables, either quantitative or qualitative, for relatives of cases are contrasted with those of control relatives. This design can be used to examine familial aggregation, contribute to identification of genetic subtypes, and test the discrete versus continuous spectrum hypothesis for disorders of unknown etiology. However, the statistical independence assumption required by conventional case-control studies is violated for observations from related individuals who share the same genetic/environmental conditions. Consequently, ignoring dependence among related subjects will lead to incorrect sample size calculations and potentially erratic scientific conclusions. In this paper, we discuss several statistical issues that are relevant to the case-control/family sampling design with a focus on the use of this design in psychiatric research. Specifically, we 1) discuss the relative merit of matched versus unmatched designs; 2) present statistical methods that are useful for analyzing family data and 3) present sample size formulas for studies of quantitative and qualitative traits. A genetic epidemiologic study of schizophrenia is used for illustrative purposes.